The recirculation of flue gases is a technology which can be used for diverse purposes in gas turbines. Flue gas recirculation is proposed, for example, for reduction of NOx emissions (nitrogen oxide emissions which are produced during combustion) or for a reduction of the flue gas flow which is to be discharged. During the recirculation of flue gases in a gas turbine, an essential proportion of the flue gas is branched from the overall flue gas flow and, after being cooled and scrubbed, can be fed to the intake mass flow of the gas turbine or to the compressor, wherein the recirculated flue gas flow is mixed with fresh air, and this mixture is then fed to the compressor.
As a result of flue gas recirculation, the carbon dioxide partial pressure in the flue gases can advantageously be increased in order to increase the carbon dioxide concentration in the flue gases and therefore to reduce the power losses and efficiency losses of power plants with carbon dioxide separation. In addition, flue gas recirculation has been proposed for reducing the oxygen concentration in the intake gases of gas turbines in order to reduce the NOx emissions.
For flue gas recirculation, U.S. Pat. No. 7,536,252 B1, for example, describes a method for controlling a flue gas recirculation flow of a turbomachine, which is recirculated, via a flue gas recirculation system, to the intake of the turbomachine. In this method, a setpoint flue gas recirculation ratio is determined, wherein the flue gas recirculation ratio is defined as a ratio of the recirculated flue gas flow to the intake flow of the turbomachine, and the actual value is adjusted to the setpoint value.
By activating flue gas recirculation or by altering the flue gas recirculation flow, the boundary conditions for operating the gas turbine are changed so that the power plant no longer demonstrates the anticipated performance or no longer achieves the anticipated power and efficiency targets when using a known operating concept, as is known from EP0718470, for example.